Exception handling.

src/main.cr

@@ -273,7 +273,8 @@ authd_storage = "storage"
 authd_jwt_key = "nico-nico-nii"
 authd_registrations = false
 
-OptionParser.parse do |parser|
+begin
+	OptionParser.parse do |parser|
 		parser.banner = "usage: authd [options]"
 
 		parser.on "-s directory", "--storage directory", "Directory in which to store users." do |directory|
@@ -293,9 +294,17 @@ OptionParser.parse do |parser|
 
 			exit 0
 		end
+	end
+
+	AuthD::Service.new(authd_storage, authd_jwt_key).tap do |authd|
+		authd.registrations_allowed = authd_registrations
+	end.run
+rescue e : OptionParser::Exception
+	STDERR.puts e.message
+rescue e
+	STDERR.puts "exception raised: #{e.message}"
+	e.backtrace.try &.each do |line|
+		STDERR << "  - " << line << '\n'
+	end
 end
 
-AuthD::Service.new(authd_storage, authd_jwt_key).tap do |authd|
-	authd.registrations_allowed = authd_registrations
-end.run
-